1. Technical Field
The present invention relates to a dispensing method.
2. Related Art
PCR (polymerase chain reaction) is an established technology in the biochemical field. With recent improvement over amplification accuracy and detection sensitivity in the PCR method, even an extremely small amount of a specimen (such as DNA) has been amplified, detected, and analyzed.
It is preferable that the PCR method uses only a small amount (volume) of a reaction liquid in view of cost and efficiency, considering the fact that the specimen and reagent employed for the PCR method are often rare and expensive. Therefore, such a technique which only requires the smallest possible amount of a reaction liquid for the PCR method has been demanded.
JP-A-2004-025148 discloses a method for handling a small amount of liquid, for example. According to this method, a target liquid is sent through a narrow tube with the aid of a sending liquid not miscible with the target liquid but separable in phase therefrom. Moreover, JP-A-2007-175002 proposes a gene analyzing device which performs PCR by shifting a PCR reaction liquid within a channel, and a method for using this device. According to the techniques disclosed in these references, the volume of the target liquid to be handled is larger than 0.5 μL (microliter), wherefore the target liquid has been otherwise prepared separately on a larger scale. For preparation of the target liquid, therefore, an instrument or an experimental tool available on the market has been used, for example.
However, particularly for PCR recently developed, preparation of the target liquid of a volume around 1 μL has been required with improvement over micro-reaction technologies and the increasing demand for cost reduction. For meeting this requirement, an accurate volume of solution containing specimens and reagents in nanoliters (less than 1 μL) needs to be measured, sent, and handled in various ways. However, the dispensing method used in the techniques of the above references or the like is difficult to handle this volume of liquid with sufficient accuracy. Even when a manually operated pipet, which is regarded as a relatively accurate tool, is used for preparation of the target liquid, for example, a volume of liquid as small as less than 0.2 μL is difficult to be measured, sent, and dispensed with sufficient accuracy. Moreover, liquid of an amount as small as on the scale of microliters or nanoliters (less than 100 μL) partially evaporates in some cases during measurement, dispensation or other processes. In this case, the amount of the liquid or the concentration of the solutes changes.